Protection of roadbeds from water seepage

ABSTRACT

AN IMPERMEABLE MEMBRANE IS ATTACHED TO THE SIDES OF THE PAVING LAID UPON A ROADBED AND EXTENDS DOWNWARDLY AND OUTWARDLY UNDERNEATH THE SOIL ADJOINING THE PAVING TO PREVENT WATER FROM SEEPING INTO THE ROADBED. THE MEMBRANE CAN EXTEND DOWN UNDERNEATH SEVERAL FEET OF EARTH AND, IN SOME INSTANCES, DEPENDING UPON THE CONTOUR OF THE   ADJOINING SOIL IT MAY BE DESIRABLE TO LAY DRAIN CONDUITS UNDERNEATH THE ROAD SURFACE TO DRAIN ANY WATER WHICH MAY SEEP UNDERNEATH THE LOWER PART OF THE MEMBRANE AND UNDER THE PAVING.

Sept. 28; 1971 o. w. GAGLE EI'AL 3,608,443

PROTECTION OF ROADBEDS FROM WATER SEEPAGE Filed May 26, 1969 2Sheets-Sheet 1 INVENTORS FIG. 4 0w. GAGLE BY H.L. DRAPER A T TORNE YSSept. 28, 1 971 o. W. GAGLE ErAL 3,608,443

PROTECTION OF ROADBEDS FROM WATER SEEPAGE Filed May 26, 1969 2Sheets-Sheet l FIG." 5

F/5 5 mvsmons 0.w. GAGLE BY H. DRAPE R A T TORNE VS United States Patent3,608,443 PROTECTION OF ROADBEDS FROM WATER SEEPAGE Duane W. Gagle andHomer L. Draper, Bartlesville, Okla, assignors to Phillips PetroleumCompany Filed May 26, 1969, Ser. No. 827,660 Int. Cl. EOlc 9/00 US. C].9422 Claims ABSTRACT OF THE DISCLOSURE An impermeable membrane isattached to the sides of the paving laid upon a roadbed and extendsdownwardly and outwardly underneath the soil adjoining the paving toprevent water from seeping into the roadbed. The membrane can extenddown underneath several feet of earth and, in some instances, dependingupon the contour of the adjoining soil it may be desirable to lay drainconduits underneath the road surface to drain any water which may seepunderneath the lower part of the membrane and under the paving.

BACKGROUND OF THE INVENTION This invention relates to roadbedconstruction and to the control of water migration in soils adjoiningthe roadbeds. In accordance with another aspect, this invention relatesto a method of preventing Water from seeping into roadbeds fromadjoining soil areas, especially planted areas, by placing animpermeable between the roadbed and the adjoining soil area. Inaccordance with a further aspect, this invention relates to roadwayconstruction wherein an impermeable membrane is placed between the sidesof paving and the roadbed upon which the paving is laid and adjoiningsoil which has a tendency to permit water to under-mine the paving. Inaccordance with a further aspect, this invention relates to the placingof an impermeable membrane formed from polymeric materials or apolymeric fabric coated with asphalt which is placed between soiladjoining paving and underneath the soil a substantial distance awayfrom the paving to prevent water from seeping into the roadbed andundermining the paving.

The problem of moisture infiltration under roadways has proved to be asevere one. Observation made during recent pavement repairs at servicestation and restaurant locations on a turnpike revealed that surfacewater from large planter areas and grass-covered islands with curbs is amajor cause of pavement failure. Water from the planted areas seepsunder the curbs and gutters and into the granular base. Freeze and thawcycles plus heavy truck trafiic result in pavement failure and costlyrepairs.

In accordance with the invention, it is proposed to install a waterimpervious mebrane along the side walls and bottoms of soil areas,especially planted areas, adjoining paving along the inside walls andbottoms of the soil area to prevent water from weakening the road base.

Accordingly, an object of this invention is to provide a method forpreventing water from seeping into roadbeds and undermining pavementlaid thereon.

Another object of this invention is to provide improved roadconstruction adjacent to a soil area having a tendency to permit waterto drain under and undermine the paving whereby the seepage of water isminimized.

Another object of this invention is to provide a water impermeablemembrane between roadbeds and adjoining soil areas.

Another object of this invention is to provide an impermeable waterbarrier between planted areas and adjoining roadways.

A further object of this invention is to provide relatively 3,6fi8A43Patented Sept. 28, 1971 inexpensive but effective Water barriers betweenroadways and adjoining soil areas to prevent water seepage into theroadbed.

Other objects and aspects, as well as the several advantages of theinvention, will be apparent to those skilled in the art upon readingthis disclosure and the appended claims.

STATEMENT OF THE INVENTION In accordance with the invention, animpermeable membrane is laid underneath the soil adjoining paving andalongside the roadbed and paving between the soil to prevent water fromseeping into the roadbed from the adjoining soil area.

In accordance with one embodiment, the impermeable membrane is attachedto the sides of the paving and extends downwardly several feet into theearth and then outwardly a substantial distance from the roadbed so asto prevent water from seeping into the roadbed and undermining thepaving.

In accordance with another embodiment of the invention, drain conduitsare provided in the soil area to permit carry-off of excess water andprevent buildup of water in the soil area which could sour the roots ofplants that may be planted in a soil area adjoining the roadway.

The invention is applicable to single roadways to prevent water seepagefrom either or both sides of the road from adjoining soil into theroadbed or it can be used in multiple roadways having flat, raised, ordepressed median strips comprised of soil which may be planted.

In accordance with presently preferred embodiments, the water imperviousmembrane is comprised of a polymeric film, preferably a thermoplasticpolymeric film, or it can be a polymeric fabric coated with an asphalt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As indicated above, theinvention relates to methods and construction for preventing moisturefrom seeping into roadbeds upon which paving is laid. A liquidimpervious membrane is used to prevent the liquid, especially water,from penetrating the roadbed and undermining the paving. The imperviousmembrane can be made of plastic film such as polyethylene,polypropylene, nylon, polyesters, and the like. The impervious membranecan also be made of fabrics such as those made of thermoplastic polymerssuch as polyethylene, polypropylene, nylon, polyesters, and the like.When employing a polymeric fabric, it is preferably impregnated withasphalt. The asphalt is preferably applied as a water emulsion. Theasphalt can be dispersed in hydrocarbon such as kerosene or distillate.

The plastic films that can be employed ordinarily will be of a 3 to 25mil thickness. The films can be oriented or unoriented polymericfilms.The films can be prepared by any of the known techniques for thefabrication of films of desired thickness and sizes.

It is presently preferred to employ polymeric fabric materials since itis generally more pliable and more easily manipulated and fabricated infield operations. The fabric can be sewed in place during roadconstruction to provide the proper fitting or form desired; instead ofsewing, if desired, the membrane can be overlapped. When overlapping isused to join adjacent sections of membrane, an emulsified asphalt can beused to seal the sections together by overlapping the sections andapplying the asphalt between the overlapped sections.

In some instances prior to applying an impervious membrane according tothe invention to a roadbed, it may be desirable to seal the roadbedfirst with an asphalt emulsion. The sealing asphalt emulsion can beeither an aqueous emulsion or a cutback petroleum emulsion. Cutbackpetroleum emulsion is asphalt emulsified in a hydrocarbon such askerosene or fuel oil. Emulsifying agents such as cationic, anionic ornonionic can be used. Cationic agents are preferred because they appearto provide a stronger adherence to both the fabric and the soil.

In one embodiment of the invention, there is provided as a membrane fora roadway a laminate system consisting of a polyolefin, e.g.,polypropylene, fabric impregnated with an asphalt-like material, e.g.,asphalt. Also according to the invention, a layer of the fabric and alayer of film can be combined with an asphalt-like material. Thus, afilm of polypropylene or polyethylene can be corn-posited with a fabricof polypropylene or polyethylene, or any combination of polyolefins orother polymers or copolymers, fabric or film can be used. Substitutionof fabric and/or film can be made upon mere routine testing of theparticular material, its structure and the intended use. Thenow-preferred fabric is a polypropylene fabric such as Lo-ktuft.

Loktuft is a nonwoven fabric of polypropylene fibers and is availablefrom Renovah Spinning Mills, Trenton and Castor Avenues, Philadelphia,Pa. 19134. Loktuft is available in rolls of about six feet width andlengths of about 200 to 300 lineal feet. Loktuft has a Weight of aboutfour to six ounces per square yard, a tensile strength of the warpdirection of 80-90 pounds and a tensile strength in the fill or woofdirection of about 90-100 pounds. Loktuft, we have found, will hold upto about four times as much asphalt material as will burlap mats, cottonfibers, woven cloth, etc.

The preferred film now is polyethylene since the combination of it withthe above-described fabric has yielded desirable results.

The asphaltic material can be applied to the fabric by impregnation,painting, spraying or any other manner in which such materials areordinarily applied. Preferably, the fabric is positioned in place andthen sprayed with sufficient asphaltic material, for example, an asphaltemulsion, to embody the fabric into the asphalt.

The asphalts used in the preparation of the emulsion include any ofthose bituminous materials used heretofore and known in the prior art,such as natural asphalts or those derived from petroleum refining, forexample, by steam refining and/or air blowing, and the like. Asphaltscharacterized by penetrations (ASTM D-51) from 0 to about 300 or evenhigher and preferably from about 40 to 300* and having softening points(ASTM D'36-26) in the range of 90 to 250 F., and preferably 100 to 150 Frepresent suitable asphalts that can be employed.

The relative amounts of the various components of the asphalt emulsionscan vary, but in general the asphalt is present in an amount in therange of 50 to 70, preferably 60 to 65 weight percent; the emulsifier ispresent in an amount in the range of 0.1 to 4, preferably 0.25 to 1; andwater is present in the amount between 50 and 25, preferably 3239 weightpercent based on the total blend.

The asphalt emulsions employed can be prepared by any method known tothose skilled in the art, for example, by preparing a soap solutioncomprising water, either soft or hard, and an emulsifying agent, eithercationic, anionic, or nonionic. The soap solution is then mixed in acolloid mill or the like with the asphalt phase, the latter beingpreferably heated to reduce the viscosity. Usually the emulsifiers andany modifiers or promoters are dispersed in the Water to form a soapsolution which is then warmed to a temperature of 90 to 200 F.,preferably 90 to 125 F. The asphalt can be heated to a temperature inthe range of 150 to 350 F., preferably 250 to 300 F. The warm soapsolution and hot asphalt are then proportioned to a colloid mill toemulsify the mixture during which milling the temperature of the mixturecan be in the range of 100 to 210 F., preferably 150 to 200 F. Thecompleted emulsion is then cooled to a temperature below 150 F. beforebeing used or transferred to storage. The method of preparing anemulsion will have some effect on the properties thereof and the in- 4tended application or utility of the emulsion will dictate whichparticular method one should use to get the desired properties.

The emulsifying agents employed to prepare the asphalt emulsion can becationic, anionic, or nonionic, or combinations thereof.

Typical of the cationic emulsifying agents which can be used in theinvention are salts of organic bases characterized by the presence of atleast one basic nitrogen atom in the cationic portion and where thelatter contains a long chain aliphatic hydrocarbon radical of at least12 and as many as 24 carbon atoms, preferably a straight chain fattyaliphatic group. A particularly useful subclass of such cationicemulsifying agents are the tetra substituted quaternary ammoniumcompounds which are well known in the art for use in preparing cationicasphalt emulsions.

Typical of the nonionic emulsifying agents which can be used, and whichare Well known in the art, include those of the general formula:

where R is selected from the group consisting of hydrogen, aryl, andalkylaryl radicals; x, y and z are integers such that (1) when x iszero, -y is also zero, and z is in the range of 6 to 11, inclusive, andsaid R is one of said aryl and alkylaryl radicals, and (2) when x and yare each greater than zero, the sum of x and z is in the range of 20 to40, inclusive, and y is in the range of 40 to 60, inclusive.

Typical of the anionic emulsifying agents which can be used include thesulfonates, particularly and alkylaryl sulfonates such as =noriso-p-octyl-phenoxy-poly(ethylene oxy) ethanol sodium sulfonates; andthe sulfates, such as ammonium lauryl sulfate, all well known in theart.

These emulsions can be made so that they are stable for storage andtransportation, yet will break rapidly when applied. Well knowncoagulating agents or electrolytes can be employed to aid in thebreaking of the emulsion and applied to the surface to be treated.

In a preferred composition, the sealing asphalt emulsion can be anaqueous asphaltic emulsion which contains from 30-50 percent Water byweight, the amount of Water depending upon the type of soil in theroadbed. If the soil in the roadbed is highly permeable, theconcentration of water in the asphaltic emulsion will be decreased. If acutback petroleum asphalt emulsion is employed, the concentration of thepetroleum dispersing agent can range from 10 to 15 percent by weight.

In actually carrying out the sealing of a roadbed with an asphalticemulsion as defined above, after the sealing agent has been added andhas cured for 12 to 24 hours the polymeric fabric is applied and it iscoated with either an aqueous asphalt emulsion or a cutback petroleumasphalt emulsion. The aqueous emulsion can contain 30- 35 weight percentwater and can possibly be as high as 50 weight percent. The petroleumcutback emulsion usually has from 10 to 25 percent by weight petroleumoil and can be as high as 50 weight percent. After the fabric has beencoated and allowed to cure for 12 to 24 hours, additional coats ofasphalt can be applied. Usually the aqueous asphalt is used because itis easier to handle and cures faster.

in some instances it is desirable to add to the coats of asphalt appliedto the polymeric fabric fillers with high surface areas such asasbestos, vermiculite, diatomaceous earth and petroleum coke. Thesefillers reduce the flow of asphalt and increase the resistance toimpact. If the membrane should be exposed to the atmosphere, the fillerprovides resistance to weathering. If asbestos filler is used, themembrane will be subject to permeation by gases and vapors andimpermeable to the flow of liquid. This is advantageous in cases wherebubbles of gases and vapor appear under the surface of the membrane.

The impermeable membrane, according to the invention, preferably extendsfrom grade elevation of the soil and paving several feet into the earthand then outwardly a substantial distance away from the roadbed toprevent seeping of water from the adjoining soil area into the roadbed.In many installations, especially around service stations and otherareas along interstate highways, the adjoining soil area contains anumber of plants and the grade elevation of this soil area usuallycorresponds to the elevation of the curb or paving surface, whichever ishigher. In most installations, the sides of the paving will be boundedby a curb and gutter and the planted area will abut against the curb andbe at the same top elevation or grade elevation as the top of the curb.Generally, the membrane will be placed anywhere from about 12 inches totwo or three feet below the top of the soil and top of the paving orcurbing bounding the paving. The membrane will extend outwardly awayfrom the roadbed a substantial distance, say 10 to 15 feet, that is, asubstantial distance between other roadways or in the case of multipleroadways the membrane can extend from one roadway to the other beneaththe soil median strip.

A better understanding of the invention will be attained upon referenceto the accompanying drawings wherein:

FIG. 1 is a typical installation of an impermeable membrane between aroadway bounded by a curb and gutter and an adjoining planted soil areahaving the same top elevation as the curbing;

FIG. 2 is a typical installation for an impermeable membrane extendingbetween two roadways with a depressed median between the two roads;

FIG. 3 is a typical installation for an impermeable membrane extendingbetween two roadways having between the roads a raised median;

FIG. 4 is an installation for a depressed median between spaced roadwaysprovided with a drain to remove excess water trapped between theroadways above the impermeable membrane;

FIG. 5 is another embodiment for multiple roadways provided with adepressed median between the roadways and a drain for removing Waterfrom the depressed median area away from the roadway system;

FIG. 6 is a schematic view of one type of drain that can be used forremoval of water from a median area between roadways;

FIG. 7 is another embodiment for a median strip provided with drainageareas between plural roadways wherein a portion of the median is raisedand the areas adjacent to the roadways are depresed to provide waterflow and drain-off areas; and

FIG. 8 is another embodiment for a raised median between roadwayswherein the water drainage from the raised median is onto the roadwaysadjacent the median strip.

Referring now to FIG. 1, the surface of the road for paving 10 is laidupon granular base 11 and earthen roadbed 12. The sides of the pavingare bounded by a curb and gutter element 13. The adjoining soil area 14contains tree 15 and grass and other plants. The grade elevation of thesoil area corresponds to the grade elevation of curb 13.

Positioned between curb and gutter 13 and soil area 14 is a polymericfilm or polymeric fabric coated with asphalt impermeable membrane 17.The membrane extends from the top of curb 13 downwardly into the earthapproximately two feet and then extends outwardly away from granularbase 11 and roadbed 12.

A perforated drainpipe which can be either metal or plastic 16 isprovided for removing water drainage trapped in the soil above membrane17 by way of pipe 16 to remove it from under the tree area out beyondthe road- Way system.

Referring to FIG. 2, there is illustrated road 20 and road 21 which canbe a part of a multiple road system and positioned between roads 20 and21 is a depressed median which can be planted, identified as 22.Approximately 12 inches below the surface of median 22 is impermeablemembrane 23 which extends between roadway 20 and roadway 21. The ends ofmembrane 23 can extend up along the ends of road 21 or the pavingportion. Roadway 21 is made up of a paving layer and a granular base 25.Similarly, roadway 20 is made up of paving 26 and granular base 27. Theends of membrane 23 can be fastened to the sides of paving 24 and 26 or,if preferred, can be laid upon the top of granular base 25 and granularbase 27 and then formation of the paving 24 and 2-6 on top of the endsof the membrane. This will permit water from seeping under the roadbedand undermining the paving. It is presently preferred to extend the endsof the membrane up alongside the ends of the paving 24 and 26,terminanting at the top of median 22. This embodiment does not include awater drain, but, as illustrated by the drawing, such is contemplated.

Referring to FIG. 3, roadway 28 and roadway 2 9 bound the raised median30. Roadway 28 is made up of paving 31 and granular base 32, whileroadway 29 is comprised of paving layer 33 and granular base 34.

Positioned approximately one foot below the surface of raised median ismembrane 35 which extends from roadway 28 to roadway 29. As described inconnection with FIG. 2, the ends of the membrane can terminate parallelto the end of the pavement at the top of the paving and soil median orcan extend beneath the paving layer and over the granular base layer asdescribed in FIG. 2. Additionally, if desired, the drain can be providedwhen necessary.

In the above embodiments it has been found that polypropylene fabriccoated with an asphalt emulsion provides a very effective waterimpermeable membrane. The polypropylene or other polymeric fabric thatcan be employed can be either a woven material, partially woven, or anon-woven fabric which can be needle punched or otherwise produced. Anon-woven polypropylene mat is very effective as a water impermeablemembrane when coated with a cationic emulsion of asphalt. The mat ismade up of oriented polypropylene fibers randomly placed on a supportingscrim. The fibers are surface fused to one another to provideomnidirectional strength. The polypropylene fibers being a non-polarhydrocarbon are readily wetted by asphalt, thus imparting the strengthof the mat to the asphalt.

Referring to FIG. 4, there is illustrated multiple roadways 36 and 37,bounding a depresed median 38 provided with a drain .39 positioned at anintermediate point in the depressed median. Positioned below the top ofmedian 38 which is soil is impermeable membrane 40 which terminatesalong the edges of roadways 36 and 37. The end of membrane 40corresponds to the top of roadways 3-6 and 37. The water drainage in thedepressed median is withdrawn by way of drain 39 and removed by way of anatural bed stream illustrated by 41.

Referring to FIG. 5, roadways 42 and 43- bound a depressed median 44which has beneath its surface at approximately one foot impermeablemembrane 45 extending between roadways 42 and 43. Again, the ends ofmembrane 45 terminate along the edges of the roadways and at the tops ofroadways '42 and 43. A drainpipe 46 extends from the top of depressedmedian 44 beneath the roadway and removes water to the far side of road43 into a ditch 47. The top of water drain 46 can be provided with asuitable grate.

In FIG. 5, the water draw-off is similar to that of water draw-offs forstreets. Either slitted or perforated iron covers can be used. Thedraw-offs can be positioned at intervals along the road. The waterflowfrom the drawoffs can be perpendicular to the roadways. These drawoffspass underneath the roadways and discharge into a ditch or a ravinealong the side of the road.

In FIG. 6, the bowl for the water draw-off extends only to the surfaceof the impermeable membrane. The membrane 48 extends from two roadwaysnot shown. The water bowl or drain 49 terminates at the interface ofmembrane 48. The membrane is covered with soil 50. The outlet for waterbowl 49 is covered with fine gravel or porous membrane to preventobjects from plugging the grate. The fine gravel is identified as 61.

Referring to FIG. 7, there is illustrated roadways 51 and 52 which boundan S-shaped raised median 53'. There are depressed areas 54 and 55adjacent to roadways 51 and 52, respectively. Water drains from theroadways and the crest of the raised median toward depressed areas 54and 55. Disposed below median 53 and depressed areas 54 and 55 is amembrane 56. The depressed median areas 54 and 55 can be provided withdrains as described above with respect to FIGS. and 6. The same type ofbowls for the water to enter can be used as those described inconnection with FIGS. 5 and 6. Water can flow from the bowl into aconduit that extends underneath both roadbeds. The conduit can alsocarry rain water from a natural stream bed as illustrated in FIG. 4. Thebowls in the various embodiments described can be connected to a conduitthat runs parallel to the roadbed and eventually discharges into aconduit such as that shown in FIG. 4 or in FIGS. 5 and 6. Thenon-permeable membrane or film in all of the figures described above isattached to the roadbed and to the drainage bowls with an adhesive suchas an asphalt or epoxy adhesive.

In a raised median such as that illustrated in FIG. 8 having roadways 57and 58 bounding a raised median 59 having disposed below the median 59an impermeable membrane 60, water flows from the raised median acrossthe roadbed.

TYPICAL APPLICATION In order to prevent shifting and erosion of thesubsurface of a roadway (e.g., a concrete highway ribbon) the followingconstruction is typical:

On each side of the concrete ribbon:

(a) Remove the earthen material from (each side of) the concrete ribbon,exposing the vertical edge of the pavement. Excavate so that there is aslope from the bottom of the vertical edge of the pavement downwardly tothe drainage ditch which parallels the pavement. (The centerline of thebottom of the ditch in this example is about 4 feet below the level ofthe road and about 12 feet from the edge of the ribbon.)

(b )The sloping surface, prepared in (a), is covered with a non-wovenpolypropylene fabric (Loktuft (TM)). The fabric can be joined at itsedges by such as sewing in order to make a continuous piece over theexcavated surface. The fabric is placed so that its upper edge will beagainst the vertical surface of the pavement and its lower edge isadjacent the ditch. The in-place fabric is coated or saturated with anasphaltic material, preferably a cationic asphalt emulsion. The emulsionis applied in an amount of about /2 gallon per square yard of fabric.Also, the fabric is sealed to the vertical edge of the pavementpreferably with the same cationic asphalt emulsion. If desired, thefabric can be treated with the emulsion prior to laying it in place.

Immediately or after aging the emulsion up to 24 to 48 hours, theearthen material is replaced, covering the now water-impermeablemembrane. The earthen material is contoured as desired between theroadway and the ditch.

The membrane will be covered by the earthen material 0 the pavementwhich would result in shifting and erosion of this subsurface withultimate roadway failure.

We claim:

1. A method for preventing moisture from seeping from adjoining earthenmaterial into a roadbed upon which paving is laid and where the earthenmaterial and paving have substantially the same grade elevation whichmethod comprises the steps of:

excavating said adjoining earthen material up to a depth below gradeelevation sufficient to promote growth of plants upon replacement of theexcavated earthen material along the edge of said roadbed so as toexpose the vertical edge of said paving, said excavation extendingoutwardly a substantial distance away from said roadbed and forming atrench along said roadbed,

covering said trench remaining after excavation along said roadbed witha plastic membrane which extends from the top of said paving downwardlyto the bottom of the trench and outwardly away from the roadbed saidsubstantial distance, and

filling said membrane covered trench with earthen material so that uponreplacement of the excavated earthen material the grade elevation of theearthen material and paving are substantially the same.

2. A method according to claim 1 wherein the trench after excavation iscovered with a membrane formed by coating said trench with an asphaltemulsion to seal the trench walls, allowing said asphalt emulsion coatto dry, applying a polymeric fabric to the asphalt coated trench, andapplying an asphalt emulsion to the polymeric fabric to form saidmembrane prior to filling said trench with earthen material.

3. A method according to claim 1 wherein the edge of said paving isbounded by a curb and gutter and the grade elevation of said earthenmaterial adjoining said curb is essentially the same as the top of saidcurb and further wherein said trench is sealed by application of anasphalt emulsion before applying said plastic membrane.

4. A method according to claim 1 wherein said plastic membrane is apolymeric film formed from polyethylene, polypropylene, nylon, andpolyesters or a fabric material formed from at least one of the samepolymers, which fabric is coated with asphalt, and said earthen materialis excavated up to a depth of about 4 feet below grade elevation.

5. A method according to claim 1 wherein said earthen material is aplanted area and a drain is placed in the bottom of said trench toremove water trapped by the membrane disposed below the surface of theearthen material and which drain carries the water away from the earthenmaterial and prevents collection of water above the membrane.

References Cited UNITED STATES PATENTS 1,421,901 7/1922 Brotsch 94-101,507,282 9/1924 Hammatt 94-10 2,020,083 11/1935 Schmid 94-33UX2,153,393 4/1939 Robertson 94-33 2,211,649 8/1940 Drury 944 2,737,092 3/1956 Gramelspacher 94-4 FOREIGN PATENTS 517,831 10/1955 Canada 94-4JACOB L. NACKENOFF, Primary Examiner US. Cl. X.R. 94-4, 33

